r1.1
                                                                                                                                                                                                                                       
                                                                                                                                                                                                                                   r1.2
                                                                                                                                                                                                                                       
       l1                                                                                                                                                                                                                              
                                                                                                                                                                                                                                       
                                                                                                                                                                                                                                       
                                                                                                      root                                                                                                                         r2  
                                                                                                                                                                                                                                       
                                                                                                                                                                                                                                       
       l2                                                                                                                                                                                                                              
                                                                                                                                                                                                                                       
                                                                                                                                                                                                                                       
                                                                                                                                                                                                                                   l3.1
                                                                                                                                                                                                                                   l3.2